Fabrication of both refractive and diffractive optical elements on the same side of a wafer is desirable for numerous applications. However, known wafer level creation techniques do not allow for high fidelity patterning of both refractive and diffractive optical elements on the same side of the wafer.
For example, if the diffractive optical element is created first, the creation of the refractive optical element will degrade the fidelity of the diffractive optical element. This degradation is due to the etching of the diffractive optical element further into the substrate that occurs during the etching of the refractive optical element.
If the refractive optical element is created first, then the high fidelity diffractive optical elements are severely degraded. Also, the topology of the refractive optical element will not allow a high quality thin photoresist layer to be spun onto the substrate. Such a high quality, i.e., uniform, thin photoresist layer is also needed to insure the creation of high fidelity diffractive optical elements. One possible solution is the use of spray coating and projection patterning, but this is not as practical as spinning the photoresist.
Thus, current lithographic techniques do not permit high fidelity patterning of both refractive and diffractive optical elements when both are to be provided on the same side of the wafer.
More generally, the above problem arises when a pattern is to be etched into a same surface already containing features which would be affected by the etch process. The larger, i.e., deeper, the feature to be etched, the more likely the etch process will effect the other features already present.